With the development of science and technology, mobile phones, portable computer and electronic products used in cars have increasingly high requirements for miniaturization and lightness. To meet these requirements flexible printed circuit boards are replacing conventional printed circuit boards due to their thinness, toughness, flexibility and foldability, and have become more and more widely used in all kinds of electronic products.
Conventional flexible printed circuit boards comprise base films, conductive patterns disposed on two opposite surfaces of the base films and via holes for conducting at least two conductive patterns of the flexible printed circuit board. The conductive patterns are made from metal such as gold (Au) or copper (Cu) etc, and serve to conduct current through the via holes in the flexible printed boards. The via holes are comprised of copper holes in the copper film, and film holes in the base film. In this particular invention via holes are referred to as film holes.
The base film is generally made from polyimide (PI) or polyethylene terephthalate (PET). Polyimide materials are flame-resistant, stable in physical dimension, with high tensile strength and thermostability. PET has properties similar to PI but have lower dielectric constant and cannot withstand high temperatures.
Conventionally, film holes are formed by a laser-ablation process using a laser irradiation apparatus. FIG. 9 shows a schematic view of a laser irradiation apparatus with a single irradiation hole. The laser irradiation apparatus 100 comprises a laser system 110 and a driving system 120 disposed adjacent to the laser system 110. The driving system 120 comprises a wrap reel 121 and a corresponding take-up reel 122. A base film 123 is wrapped around the wrap reel 121. During operation the base film 123 is taken up by the take-up reel 122 thereby moving the base film 123 between the wrap reel 121 and the take-up reel 122. The base film 123 is made of either polyimide or polyethylene terephthalates. Referring to FIG. 10, a plurality of sprocket holes 1231 are disposed along lateral sides of the base film 123 so as to help the movement of the base film 123 between the wrap reel 121 and the take-up reel 122. In this way, film holes can be formed in the base film 123 continuously. Referring to FIG. 11, a plurality of film holes 1232 are formed therein.
The above laser irradiation apparatus 100 involves only a single irradiation process, thereby each desired film hole 1232 will require a positioning step, which is both time-consuming and un-conducive to mass production.
Referring to FIG. 12, another laser irradiation apparatus 200 with multiple irradiation holes is shown. The laser irradiation apparatus 200 is similar to the laser irradiation apparatus 100 in FIG. 9, but with an additional photo mask 201. The photo mask 201 has holes corresponding to the desired pattern defined in it, thus enabling a desired pattern to be created when forming the film holes. Therefore, one laser flash produced by the laser irradiation apparatus 200 can form multiple film holes in the base film 223.
However, residue tends to remain in the film holes after laser ablation and can be difficult to remove. In addition, during laser ablation ashes may also be created, these may then escape outwards in all directions and can reach a height of about 1 centimeter. Ashes may also reach the photo mask 201 above the base film 123 and bring residual heat thereto. The photo mask 201 may therefore suffer from shape distortion, which will effect precision and lead to a decrease in quality of production. Furthermore, it is difficult when using the laser ablation method to precisely control depth of the film holes. Moreover, since with a single focus only a single or particular number of film holes can be obtained, production efficiency is relatively low, and is therefore still not favorable for mass production.
Therefore, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.